
The version of the software used to create the tarball and the packages
can be set with the 'version' option. If the version is not explicitely
set, then it is determined automatically in the following way :

- If the +version_command+ option is set, then the value of this option
  is run in the checked out source tree, and the output is used as the
  version.

- If the +version_command+ is not set, or if running the command failed,
  then the most recent tag (as returned by git-describe) is used as
  version.

